Zhao-Sha Meng

Polynuclear and polymeric gadolinium acetate derivatives with large magnetocaloric effect.

Two ferromagnetic μ-oxo(acetate)-bridged gadolinium complexes [Gd(2)(OAc)(2)(Ph(2)acac)(4)(MeOH)(2)] (1) and [Gd(4)(OAc)(4)(acac)(8)(H(2)O)(4)] (2) and two polymeric Gd(III) chains [Gd(OAc)(3)(MeOH)](n) (3) and [Gd(OAc)(3)(H(2)O)(0.5)](n) (4) (Ph(2)acacH = dibenzoylmethane; acacH = acetylacetone) are reported. The magnetic studies reveal that the tiny difference in the Gd-O-Gd angles (Gd···Gd distances) in these complexes cause different magnetic coupling. There exist ferromagnetic interactions in 1-3 due to the presence of the larger Gd-O-Gd angles (Gd···Gd distances), and antiferromagnetic interaction in 4 when the Gd-O-Gd angle is smaller. Four gadolinium acetate derivatives display large magnetocaloric effect (MCE). The higher magnetic density or the lower M(W)/N(Gd) ratio they have, the larger MCE they display. Complex 4 has the highest magnetic density and exhibits the largest MCE (47.7 J K(-1) kg(-1)). In addition, complex 3 has wider temperature and/or field scope of application in refrigeration due to the dominant ferromagnetic coupling. Moreover, the statistical thermodynamics on entropy was successfully applied to simulate the MCE values. The results are quite in agreement with those obtained from experimental data.

Pure Trinuclear 4 f Single-Molecule Magnets: Synthesis, Structures, Magnetism and Ab Initio Investigation

A family of linear Dy(3) and Tb(3) clusters have been facilely synthesized from the reactions of DyCl(3), the polydentate 3-methyloxysalicylaldoxime (MeOsaloxH(2) ) ligand with auxiliary monoanionic ligands, such as trichloroacetate, NO(3)(-), OH(-), and Cl(-). Complexes 1-5 contain a nearly linear Ln(3) core, with similar Ln···Ln distances (3.6901(4)-3.7304(3) Å for the Dy(3) species, and 3.7273(3)-3.7485(5) Å for the Tb(3) species) and Ln···Ln···Ln angles of 157.036(8)-159.026(15)° for the Dy(3) species and 157.156(8)-160.926(15)° for the Tb(3) species. All three Ln centers are bridged by the two doubly-deprotonated [MeOsalox](2-) ligands and two of the four [MeOsaloxH](-) ligands through the N,O-η(2)-oximato groups and the phenoxo oxygen atoms (Dy-O-Dy angles=102.28(16)-106.85(13)°; Tb-O-Tb angles=102.00(11)-106.62(11)°). The remaining two [MeOsaloxH](-) ligands each chelate an outer Ln(III) center through their phenoxo oxygen and oxime nitrogen atoms. Magnetic studies reveal that both Dy(3) and Tb(3) clusters exhibit significant ferromagnetic interactions and that the Dy(3) species behave as single-molecule magnets, expanding upon the recent reports of the pure 4f type SMMs.

Symmetry related [DyIII6MnIII12] cores with different magnetic anisotropies

Two heterometallic [DyIII6MnIII12] clusters comprising of the same [MnIII8O13] fragment, four isolated MnIII ions and two linear [DyIII3] units have been synthesised. Except for the same composition, the main difference of these two cores lies in the coordination environment and the orientations of the linear [DyIII3] units. This difference leads to an alternation in the symmetry of the two cores that significantly modulates their magnetic properties including ground spin state and slow relaxation behavior.

Study of a magnetic-cooling material Gd(OH)CO3

The magnetocaloric effect of a coordination polymeric material with a repeating unit of Gd(OH)CO3 has been studied experimentally using isothermal magnetization and heat capacity measurements. The maximum entropy change, −ΔSm, reaches 66.4 J kg−1 K−1 or 355 mJ cm−3 K−1 for ΔH = 7 T and T = 1.8 K. Density functional theory (DFT) calculations show weak and competing antiferromagnetic interactions between the metal centres.

Tuning the Spin States of Two Apical Iron(II) Ions in the Trigonal‐Bipyramidal [{FeII(μ‐bpt)3}2FeII3(μ3‐O)]2+ Cations Through the Choice of Anions

When located in octahedral environment, the iron(II) ion with a d electronic configuration may adopt two different stable electronic states, namely, a diamagnetic low-spin (LS) state and a paramagnetic high-spin (HS) state, which both give rise to different magnetic, optical and electronic properties. So tuning the spin state of the iron(II) ion is significant and contributes to the development of amazing materials that can be used as molecular switches, sensors and display devices. As is well established, the spin state depends on relative strength of spin paring energy (P) and splitting energy (D0). If the former is much stronger than the latter, the HS state will be stabilised, and if D0 is stronger then the LS state will be the ground state. If P and D0 are comparable a spin crossover (SCO) may occur between the HS and LS state by external perturbations such as temperature, pressure or light irradiation. So the main task is to make a judicious choice of ligand, which can impose a proper ligand-field strength. However, in reality, the spin state of the iron(II) ion is quite sensitive to even more subtle changes such as solvent molecules, polymorphism and counterions. As one of the best representatives of switchable molecules, SCO materials have attracted considerable interest in the chemistry and materials fields. Current work mainly focuses on the enhancement of cooperativity, which results in an abrupt transition and a wider thermal hysteresis. Another promising research area, but with few examples, is the combination of magnetic-exchange and spin-transition (ST) phenomena in the same molecule or polymeric network, which could eventually afford new switching materials with considerable amplification of the response signal. Much more work should be done to expand our knowledge of spin electronics. To induce a ST, the most common method is by varying the temperature. However, light-and pressure-induced SCOs play an increasingly important role owing to their potential applications as optical and pressure switches, for example. Moreover, the latter two methods are not restricted to thermal SCO compounds: LIESST (light-induced excited spinstate trapping) may also be observed in LS compounds, whereas HS compounds may experience STs with the application of external hydrostatic pressure. Although there are many examples that exhibit thermal STs, rare spin-crossover clusters of iron(II) have been found to exhibit a mixed-spin structure and synergy between ST and magnetic interaction. Fortunately, by introducing counterions, we have successfully tuned the spin states of two apical iron(II) ions in the pentanuclear [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]2+ (Hbpt=3,5-bis(pyridin-2-yl)-1,2,4-triazole) cations through anions. Both apical ions are of LS states in [{Fe ACHTUNGTRENNUNG(mbpt)3}2Fe II 3ACHTUNGTRENNUNG(m3-O)] ACHTUNGTRENNUNG(NCS)2·10H2O (1), [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3O)] ACHTUNGTRENNUNG(ClO4)2·3H2O (2) and [{FeIIACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]I2· 4MeCN (3), and are of HS states in [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3O)] ACHTUNGTRENNUNG[FeIII2ACHTUNGTRENNUNG(m-O)Cl6]·1/2H2O (4). In this new {Fe5} family, two new developments have been achieved: 1) The ligand 4amino-3,5-bis(pyridine-2-yl)-1,2,4-triazole (abpt) has been, for the first time, used to produce the oxo-centred polynuACHTUNGTRENNUNGcle ACHTUNGTRENNUNGar iron(II) complexes; 2) Two types of spin topology have been trapped in the [{Fe ACHTUNGTRENNUNG(m-bpt)3}2FeII3ACHTUNGTRENNUNG(m3-O)]2+ cluster that are controlled by counterions. Note that only one [a] X. Bao, J.-D. Leng, Z.-S. Meng, Dr. Z.-J. Lin, Prof. Dr. M.-L. Tong Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education State Key Laboratory of Optoelectronic Materials and Technologies School of Chemistry & Chemical Engineering Sun Yat-Sen University, Guangzhou 510275 (P.R. China) Fax: (+86) 20-8411-2245 E-mail : tongml@mail.sysu.edu.cn [b] Dr. M. Nihei, Prof. Dr. H. Oshio Graduate School of Pure and Applied Sciences University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8571 (Japan) Fax: (+81) 29-853-4238 E-mail : oshio@chem.tsukuba.ac.jp Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201000526.

Anion-dependent construction of copper(I/II)-1,2,4,5-tetra(4-pyridyl)benzene frameworks

The unique tetrapyridyl ligand 1,2,4,5-tetra(4-pyridyl)benzene (bztpy) isolated from previous hydrothermal in situ metal ligand reaction is found to exhibit remarkable anion-dependent assembly of a series of novel metal–organic frameworks (MOFs), [Cu2(CN)2(bztpy)] (1), [Cu(SO4)(bztpy)]·1.5H2O (2), [Cu2Br2(bztpy)]·MeCN (3) and [Cu10I10(bztpy)2]·2H2O (4), which were synthesized under hydro/solvothermal conditions. These MOFs were characterized by elemental analysis, IR and single-crystal X-ray diffraction. Compound 1 consists of [Cu(CN)]n chains that link the neighbouring ones via tetradentate bztpy bridges to form a corrugated 2D layer. When bztpy is treated with CuSO4, a 3D (3,5)-connected network 2 is obtained, in which novel [Cu(bztpy)]n ladders are interconnected by sulfate anions μ-bridges. However, Br− and I− anions assist the formation of {Cu2Br2} and {Cu10I10} SBU in the cluster-based metal–organic frameworks 3 and 4, respectively, and result in a completely different topology. Compound 3 shows a 3D PtS net, while compound 4 has a new 3D (4,8)-connected topology. A discussion of the crystal structures, as well as the coordination behaviour of the special tetrapyridyl ligand upon different geometries of the central connecter is provided. In addition, the photoluminescent properties of 1, 3 and 4 in the solid state at ambient temperature are also investigated.

Synthesis, Structure, and Photoluminescent Properties of Two New Microporous Eu(III) Coordination Polymers with 2,4,6-Pyridinetricarboxylate

Two new three-dimensional (3D) microporous Eu(iii) coordination polymers, [Eu5(pyta)5(H2O)7]·3.5H2O (1) and [Eu2(ox)1.5(pyta)(H2O)4]·4.5H2O (2) (H3pyta = 2,4,6-pyridinetricarboxylic acid, ox2– = oxalate), have been synthesized under hydrothermal conditions. The oxalate ligand in 2, generated in situ from the cleavage and chemical rearrangement of the H3pyta ligand, is incorporated to construct two kinds of 1D hydrophilic channels in 2. Both 1 and 2 show the characteristic photoluminescent properties of Eu(iii) compounds. Desolvated 2 shows interesting solvent-dependent photoluminescent properties.